1. Field of the Invention
The present invention relates to a method of securing a stator winding to an inner periphery of a stator core having no slots, and to a rotating electrical machine incorporating a slotless stator with a stator winding secured to an inner periphery of a stator core having no slots.
2. Description of the Related Art
Heretofore, as a method of securing a stator winding such as a cylindrical stator winding, to an inner periphery of a cylindrical stator core having no slots, there is known the securing method disclosed in Japanese Patent No. 2847800.
With this known securing method, at first a cylindrical stator winding is accommodated inside a stator core, and then a round rod shaped inner diameter jig made of a fluoroplastic is inserted inside the stator winding. Next, the stator core, the stator winding and the inner diameter jig are then immersed as one in a resin tank used for resin impregnating. After resin impregnating step, these are withdrawn from the impregnating resin tank as a single body and in this state the resin is heated and hardened. After this, the inner diameter jig is withdrawn from the stator winding. That is to say, with this securing method, the stator core and the stator windings are secured by the adhesive strength of the resin at the time of resin hardening.
However, with high speed rotating electrical machines where the rotor is rotated at high speed (around 100,000 rpm) inside the inner periphery of the stator winding, there is a problem from the point of efficiency, with the heat generated due to heat loss occurring in the stator winding and the stator core.
Additionally, with With the abovementioned securing method, since the inner diameter jig is made from a fluoroplastic, then even though the inner diameter jig presses against the inner periphery of the stator winding at the time of resin hardening, the outer periphery of the inner diameter jig will not deform with irregularities replicating the inner periphery of the stator winding.
Therefore, on the inner periphery of the stator winding, the resin hardens so as to form a smooth cylindrical inner surface which does not retain the irregularities of the inner peripheral surface of the stator winding. Consequently the inner peripheral surface area of the stator winding having the hardened resin thereon, which serves as a heat dissipating surface at the time of operation is reduced, and portions where the resin is thickly attached occur on the inner peripheral face of the winding, so that sufficient heat dissipation performance cannot be obtained.
The present invention takes into consideration the above situation with the object of improving heat dissipation performance of a stator winding.
In order to achieve the above object, the present invention adopts the following means. That is to say, a securing method for a stator winding according to the present invention involves securing the cylindrical stator winding to an inner periphery of a cylindrical stator core having no slots, wherein a mandrel comprising an outer peripheral pushing portion made from a resilient material for pressing an inner periphery of the stator winding is inserted with the stator winding which is inserted into the stator core, and in this condition, a thermosetting resin which is adhered to the stator winding is heat hardened.
With such a construction, when the outer peripheral pushing portion of the mandrill presses into the inner periphery of the stator winding, this outer peripheral pushing portion is deformed into irregularities replicating the inner periphery of the stator winding. Consequently, when the thermosetting resin adhered to the stator winding is heat hardened with the stator core, the stator winding and the mandrel all held together as one, the mandrel thermally expands and the outer peripheral pressing portion deforms with irregularities along the inner periphery of the stator winding. Therefore, with the inner peripheral side of the stator winding, the thermosetting resin hardens with the irregularities retained. As a result, the effective inner peripheral surface area of the stator winding is increased and heat dissipation is thus improved.
With the securing method for a stator winding according to the present invention, the outer peripheral pushing portion may be constructed by securing the resilient material to the outer periphery of the mandrel body, or by making the mandrel body itself from a resilient material. For this resilient material, a rubber such as silicone rubber or fluororubber may be used. Moreover, in the case where the resilient material is secured to the outer periphery of the mandrel body, for example, a fluoroplastic may be used for the mandrel body.
With a rotating electrical machine incorporating a slotless stator according to the present invention, where a stator winding is secured with a thermosetting resin to an inner periphery of a stator core which has no slots, an inner periphery of the stator winding has an irregular hardened surface made by hardening the thermosetting resin, along the irregular shape of the inner periphery of the stator winding.
With such a construction, heat dissipation is improved more than for the case where the inner periphery of the stator winding is formed as a smooth cylindrical surface, due to the increase in the effective inner peripheral surface area of the stator winding. Therefore, even in the case where the rotor is rotated at high speed inside the stator winding, heat generated due to heat loss is effectively cooled, and use at higher loads, that is to say higher outputs, becomes possible. That is, even with the same loss, by improving the cooling efficiency, the temperature can be kept low, and hence higher loads and higher outputs become possible for the same allowable temperature.